Eric Hsu, one of the many men behind XS Engineering and also a veteran of A'PEXi and Cosworth, got a hold of the February 2008 issue of Japan's Option magazine in which the pub strapped the MINE'S-modified Nissan GT-R to a Dynapack and ripped off a couple of runs. The GT-R was equipped with the prototype catback exhaust we featured a couple of weeks back, and although the design is far from streetable in its current form, it still created just over 20 hp over the stock setup by reducing backpressure and allowing a 1.42 psi increase in boost. Although Hsu maintains that the Dynapack might skew the results by up to five-percent, the 507.9 ps (500.95 hp) rating at the flywheel is still impressive considering that nothing was done to the GT-R's ECU.
[Source: JDM-Insider]

501 with exhaust - 20 exhaust = 481 at the hubs. 5% higer than a dynojet = 457 at the wheels, "with dynojet". So we are back to 5% total drivetrain loss which is simply not possible on this car with the extra drive shafts.

Explain why Eric Hsu, one of the many men behind XS Engineering and also a veteran of A'PEXi and Cosworth would get it wrong and say that it's at the flywheel and not the wheels, this doesn't make since to me. The guy clearly knows more about engines than almost anyone here if not everyone.

You should go and pick up a copy of the February 2008 copy of Option Magazine. Hiro the editor in chief just sent me a copy because thereís a feature of Cosworth in it. Aside from the fact that thereís a bitchin feature of Cosworth in it (and a picture of yours truly with a stupid ass smile), the main focus of this issue is the R35 GT-R. Thereís also a R35 GT-R catback exhaust test in it where some shop fabricated a titanium catback exhaust and the car made 507.9ps (500.95hp) at the flywheel. Granted, this test was conducted on a Dynapack so it probably read 5% or higher than any other dyno, but the gain of 22ps is for real. If you canít do the math, thatís 485ps from the factory which is pretty god damn buff already considering the car is rated at 480hp at the flywheel. The boost went up by 0.1kg/cm^2 (1.42psi) due to the reduced backpressure, but this also tells you that the car has some serious potential from the factory. By looking at this exhaust I can guarantee you that itís louder than hell so I wouldnít expect a 22ps gain on a production catback exhaust though.
It looks like Nissan calibrated the fuel map to go leaner after peak torque. This is done to increase peak horsepower and is probably fine at low boost and horsepower levels where the cooling effect of a rich mixture is not necessary. Keep in mind that Nissan is shooting to compete with supercars so they need that peak horsepower number so rich baller dudes can tell their buddies, ďIt makes 480hp. Thatís the same horsepower as your Porsche 997 Twin Turbo for $60k less!!!Ē. The R35 is buff.

Despite the fellow being an expert there is no way he can really have flywheel results. It is simple - the only way to have that is to have complete information about entire drive train loss (less the tires since it is a hub dyno) as a function of rpm. The only way to really get that is to test the drive train in isolation or to have the actual at the flywheel dyno results and the hub results and subtract. If he doesn't have that then he is estimating drive train loss.

Of course this contradiction weakens my point above about evidence for under-rating....

Despite the fellow being an expert there is no way he can really have flywheel results. It is simple - the only way to have that is to have complete information about entire drive train loss (less the tires since it is a hub dyno) as a function of rpm. The only way to really get that is to test the drive train in isolation or to have the actual at the flywheel dyno results and the hub results and subtract. If he doesn't have that then he is estimating drive train loss.

Of course this contradiction weakens my point above about evidence for under-rating....

Don't know much about that dyno, but many chassis dynos, including the Dynojet, allow you to do a coast down so as to get good (not perfect)approximations of friction and rotational losses. Yes, it's still an estimate, however, because such losses may not be linear to the power produced.

I got the impression from one or more of Artpe's notes and others that this particular brand of dyno allows you to simulate engine HP thru allowances for drivetrain losses.

I also saw the article. There is no mention about if the numbers were calculated or modified with coast down static drivetrain losses calculated. The article shows the car strapped to four Dynopacks at the hubs. The graphs appeared to be straight acceleration graphs with the numbers peaking at 508 ps with the exhaust and 485 ps in stock form. So, I'm assuming that drivetrain losses were not accounted for.

Unless someone has more information about how the test was done. You must assume that these numbers were at the wheel hubs. I'm guessing that Eric Hsu just mis spoke / typed.

You can also get a hint from what he wrote... 5% higher than other dynos... Dynopacks in general only lose about 10% compaired to 15% from a Dynojet because there are no rotational / frictional losses from the wheel and tire. If he meant flywheel, then he would have said 15% higher than other dynos.

No, but it does not matter. What if someone told you they made a perpetual motion machine. Would you believe them? Do you have a Ph.D. in physics with a focus on thermodynamics? See the point?

His point is Eric Hsu is just not anyone, it's someone with a decent reputation and knowledge in that field. It's like Schumacher making a statement about driving F1 cars, most people like you and me probably would'nt question him. Not to say that he's never wrong.

Unless someone has more information about how the test was done. You must assume that these numbers were at the wheel hubs. I'm guessing that Eric Hsu just mis spoke / typed.

You can also get a hint from what he wrote... 5% higher than other dynos... Dynopacks in general only lose about 10% compaired to 15% from a Dynojet because there are no rotational / frictional losses from the wheel and tire. If he meant flywheel, then he would have said 15% higher than other dynos.

I think the dyno already had a drivetrain-to-flywheel correction factor of 5% built into the report on the screen.

Here's an explanation from another forum:

Hello,

The Dynapack measures power at the axle - one of the only machines that actually does - most machines measure what the roller did, which isn't ever the same thing. The reason we have a "flywheel" screen is because most chassis dynos for years have been incorrectly displaying measured torque. We show the measured torque, because we can - we actually measure it directly.

If you have a car making 300lb/ft at the flywheel and run it through a drivetrain that has a 4:1 gear reduction, the gears will multiply the torque and divide the rpm. So your actual "wheel torque" or axle torque will be something like 1200lb/ft - minus a little bit of efficiency loss. So why do most if not all roller dynos display the torque as 300 minus a little loss? Beats me. It is completely incorrect, but those are the numbers people are used to seeing. It is probably because most roller machines are measuring the roller and back calculating everything from there - and dividing it by the engine rpm, instead of the axle RPM. Their torque numbers are calculated several steps away from the original measurement. By comparison, we measure torque at the source, and RPM at the source, so it is direct measurement. Because people aren't used to seeing 1200lb/ft of axle torque (even though it is correct) we have the "flywheel" screen. The flywheel screen takes our measured torque number and divides it by the vehicle's gear ratio to get it back to a "flywheel" torque number that people are expecting to see. True, it isn't actual flywheel torque because we aren't measuring it there - but it is much closer to being flywheel torque than wheel torque. After seeing the explanation, I think you'll see that calling 300lb/ft the "wheel torque" is ridiculous - but it has become the standard. We show you the real numbers as a default and have the Flywheel screen to show the numbers the other way if you want them. Because of all of this, most of our operators use the flywheel screen to give the torque numbers that they are expecting to see.

The TCF function is there if you want to use an estimate for drivetrain loss and add it to the "flywheel" numbers. If it is at 1.0 - nothing is done. If it is at 1.15, then the measurements are multiplied by 1.15 on the flywheel numbers only. Also, the flywheel screens show the TCF number - to discourage people from being sneaky about using it.

Sorry it is so long winded, but I think it is important to show why we do what we do so people understand it. If you have any other questions, just let me know.

Hello John,
Thank you for the detailed response to my questions. So the dyno sheet I sent shows a TCF of 1.00, does that mean that the results displayed are at the hubs, or an estimate of flywheel power with the Dynapack software adding a correction factor in?

Response:

RE: Dyno Graph Questions??
Date: Tue, 18 Dec 2007 10:55:11 -0800

Hi,

1.0 means that no correction has been added in - so it is as measured at the hubs.

Thanks,

John

IMHO the dyno graph shows the hub number with a 5% torque correction factor built in.

Thanks, this is consistent with my previous analysis as well as the N'ring regression analysis by lucid.

Quote:

Originally Posted by Swamp

My post directly following his was:

OMG how many times did I have to say it??? Totally under-rated. Even conservatively this thing has a 15% total transmission and drivetrain loss. With all the extra shafts it could be closer to 20% (more efficient maybe than a RS4 drivetrain but more shafts/bearings as well). This means the engine is putting out about 560 - 590 crank hp.

Now we know the whole story...

I also just re-ran the power to weight vs. N'Ring lap time regression with 560 hp and found it to be outperforming the linear fit by a mere 1.7 seconds. Previously, we found in the regression thread that is was 25 seconds faster than the model predicted. If the car really had that good of a driver and tires as good as I expect they are the time is ABSOLUTELY NOTHING SPECIAL. It is just like a drag car getting a good drag strip time. hp rules even at the N'Ring.

If you would stop quoting me completely out of context you would appear at least marginally "on the ball". As you know, since you participated in the bloody discussion, I admitted "massively" was both slightly premature and too aggressive of a word choice. How many times did I say this exact same thing above in those threads, 5, 10?

And by the way 45 hp is very close to 10% and that is pretty darn large.

^^^^ RIIIIIIIIIIIIIGHT. "On the ball" by what standards. The new estimates are between 21hp to 45hp under-rating, your estimates are 80hp to 110hp under-rating, you call that "on the ball", are you kidding me. I agree that 45hp is huge, but it could possibly be as low as 21hp as well. Either way, it is still under-rated if this is correct.